Vehicles may be configured with an intake air temperature sensor for estimating a temperature of fresh air entering a vehicle engine. Based on the intake air temperature, air mass and/or air volume estimations may be made, which may then be used for air-to-fuel ratio control. Likewise, vehicles may be configured with an ambient air temperature sensor for estimating a temperature of air surrounding the vehicle. Based on the ambient air temperature sensor, fuel system evaporative leak test thresholds may be adjusted. Both the intake air temperature sensor and the ambient air temperature sensor may need to be periodically diagnosed to ensure proper functionality.
One example approach for diagnosing an intake air temperature sensor is shown by Martin et al. in U.S. Pat. No. 9,114,796. Therein, a rationality check between the intake air temperature sensor and an engine temperature sensor may be performed following an engine soak. If the temperature measurements from the intake air temperature sensor and the engine temperature sensor do not agree, the vehicle speed at which an automatic engine shutoff is initiated may be lowered to prolong engine operation and thus the flow of intake air over the intake air temperature sensor. If the intake air temperature sensor still disagrees with the engine temperature, the intake air sensor may be determined to be degraded.
However, the inventors herein have recognized potential issues with such systems. As one example, such an approach does not address the rationality of the ambient air temperature sensor. Even if the ambient air temperature sensor were to be rationalized based on the intake air temperature sensor and the engine temperature sensor following the engine soak (when all sensors conceivably measure the same ambient temperature), the ambient air temperature sensor is typically located on an external component of the vehicle (such as under a side mirror) and as such may be differentially affected by environmental factors and/or not exposed to the same rejected engine heat as the internally-located intake air temperature sensor and engine temperature sensor. Further still, by requiring a subsequent engine start and subsequent duration of engine operation to confirm the rationality of the intake air temperature sensor, the approach of Martin may unduly delay accurate diagnosing of the sensors, particularly in hybrid vehicles where the engine may be operated infrequently.
In one example, the issues described above may be addressed by a method for a vehicle. The method may include, at a duration after an engine-off event, determining that an intake air temperature measured by an intake air temperature sensor of the vehicle is less than an ambient air temperature measured by an ambient air temperature sensor of the vehicle. The method may further include, in response to the determining, flowing air from a catalyst across the intake air temperature sensor and indicating the intake air temperature sensor is functional responsive to the intake air temperature converging to the ambient air temperature during the flowing. In this way, divergence between the intake air temperature sensor and the ambient air temperature sensor may be confirmed as being due to solar loading (to which the ambient air temperature sensor, but not the intake air temperature sensor, may be exposed) rather than a degraded sensor. If the intake air temperature does not converge with the ambient air temperature, the intake air temperature sensor may be determined to be degraded. As one example, the air from the catalyst may be flowed over the intake air temperature sensor by rotating the engine in reverse to ingest exhaust gas/ambient air from the exhaust system through the engine and to the intake air temperature sensor, which may include heated air housed in the catalyst and/or may include heating the air via heat retained by the catalyst. Further, in some examples, rationality of the ambient air temperature sensor may be confirmed by obtaining an ambient temperature in the vicinity of the vehicle (e.g., from a weather service and/or from ambient air temperature sensors of nearby vehicles) and comparing it to the ambient air temperature measured by the ambient air temperature sensor.
By ruling out environmental or internal sources of excess heat that may be present at the time of the rationality check, false positive identifications of sensor degradation may be reduced. Further, by relying on an engine component that may be operated during non-combustion conditions of the engine to supply the air to the intake air temperature sensor, operation of the engine to confirm the functionality of the intake air temperature sensor may be reduced or avoided, thus allowing for engine controls based on the intake air temperature sensor output to be adjusted, even at engine start-up, if sensor degradation is determined.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.